The invention generally relates to a bus coupler. More preferably, it relates to an amplitude-controlled transmitting circuit for generating an essentially rectangular active pulse in a transmitting pulse made up of an active pulse and an equalizer pulse. The bus system conveys AC voltage information and DC voltage to make available the on-board voltage of subscriber stations. For example, in building systems technology, the European Installation Bus Association, EIBA, operates using a bus system of this type.
In buildings systems technology, bus couplers, in which the bus carries AC voltage information and superimposed DC voltage for supplying the on-board networks of subscriber stations usually operate using a transformer whose volume can not be reduced to any considerable extent.
Such a bus coupler is common in a bus system in building system engineering, e.g., in accordance with EIBA. A conventional circuit arrangement for transmitting binary signals, which is described in European Patent Application No. 346 572, relates to a transmitting circuit for generating an essentially rectangular active pulse, AC voltage information and DC voltage being transmitted in order to make available on-board voltage of subscriber stations on the bus. The transmitting circuit, in each case, operates using a transmitting stage, which has a transmitting transistor in an emitter circuit, whose base is connected to the driving line.
An object of the present invention is to provide a bus coupler.
The cited objective is achieved in a bus coupler according to an embodiment of the present invention. The transmitting circuit operates using a transmitting stage, which has a transmitting transistor in an emitter circuit. The base of the transmitting transistor is connected to the driving line. To reduce the driving signal on the driving line, a reducing transistor is connected to the base of the transmitting transistor. The reducing transistor is of the inverse type with respect to the transmitting transistor. The emitter-collector path of the reducing transistor is connected in parallel to the base emitter junction of the transmitting transistor. The base of the reducing transistor is connected to the tap of a voltage divider, which at its one external terminal is connected to a reference voltage and at its other external terminal is connected to a capacitor functioning as a separating filter for the AC voltage. The capacitor is connected at its terminal to a bus connector. When transistors are mentioned here, it is only the mode of operation of such components that is meant, these components being capable of realization in integrated circuits.
In the bus coupler according to the present invention, the on-board voltage can be used as reference voltage for the voltage divider.
A more user-friendly bus coupler is achieved in a bus coupler according to another exemplary embodiment of the present invention.
In this case, a driver transistor, in accordance with its function, operates on the transmitting transistor, the driver transistor being limited in its amplitudes by the reducing transistor, a diode, in accordance with its function, being connected in series with the emitter of the reducing transistor. In this connection, the transmission amplitude is independent of the tolerance of the driving voltage at the input for the transmitting signal. It is advantageous if the transmitting circuit, operating as a control amplifier, is related, in its control threshold, to the frame potential. A substantial limiting is achieved by obtaining the control criterion through comparing the output amplitudes to the reference voltage via the voltage divider.
In order to limit the short-circuit currents, it is expedient if the transmitting transistor in its collector line has a resistor for limiting short-circuit currents.
At the connecting line between the capacitor as separating filter for the AC voltage and the voltage divider, it is advantageous to connect a receiver circuit. The receiver circuit to can advantageously have a pnp transistor in the emitter circuit and a collector resistor. The emitter of the pnp transistor is connected to the on-board voltage and its collector resistor is connected to the frame. Between the connection of the capacitor, as separating filter for the AC voltage, and of the voltage divider, on the one hand, to the receiver circuit, on the other hand, a filter can advantageously be connected for disturbances from the bus. This filter, according to a simple and advantageous embodiment, can be configured by a resistor and a capacitor.